src/net/rpc/client.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package rpc

 import (
 	"bufio"
 	"encoding/gob"
 	"errors"
 	"io"
 	"log"
 	"net"
 	"net/http"
 	"sync"
 )

 // ServerError represents an error that has been returned from
 // the remote side of the RPC connection.
 type ServerError string

 func (e ServerError) Error() string {
 	return string(e)
 }

 var ErrShutdown = errors.New("connection is shut down")

 // Call represents an active RPC.
 type Call struct {
 	ServiceMethod string      // The name of the service and method to call.
 	Args          interface{} // The argument to the function (*struct).
 	Reply         interface{} // The reply from the function (*struct).
 	Error         error       // After completion, the error status.
 	Done          chan *Call  // Receives *Call when Go is complete.
 }

 // Client represents an RPC Client.
 // There may be multiple outstanding Calls associated
 // with a single Client, and a Client may be used by
 // multiple goroutines simultaneously.
 type Client struct {
 	codec ClientCodec

 	reqMutex sync.Mutex // protects following
 	request  Request

 	mutex    sync.Mutex // protects following
 	seq      uint64
 	pending  map[uint64]*Call
 	closing  bool // user has called Close
 	shutdown bool // server has told us to stop
 }

 // A ClientCodec implements writing of RPC requests and
 // reading of RPC responses for the client side of an RPC session.
 // The client calls WriteRequest to write a request to the connection
 // and calls ReadResponseHeader and ReadResponseBody in pairs
 // to read responses. The client calls Close when finished with the
 // connection. ReadResponseBody may be called with a nil
 // argument to force the body of the response to be read and then
 // discarded.
 // See NewClient's comment for information about concurrent access.
 type ClientCodec interface {
 	WriteRequest(*Request, interface{}) error
 	ReadResponseHeader(*Response) error
 	ReadResponseBody(interface{}) error

 	Close() error
 }

 func (client *Client) send(call *Call) {
 	client.reqMutex.Lock()
 	defer client.reqMutex.Unlock()

 	// Register this call.
 	client.mutex.Lock()
 	if client.shutdown || client.closing {
 		client.mutex.Unlock()
 		call.Error = ErrShutdown
 		call.done()
 		return
 	}
 	seq := client.seq
 	client.seq++
 	client.pending[seq] = call
 	client.mutex.Unlock()

 	// Encode and send the request.
 	client.request.Seq = seq
 	client.request.ServiceMethod = call.ServiceMethod
 	err := client.codec.WriteRequest(&client.request, call.Args)
 	if err != nil {
 		client.mutex.Lock()
 		call = client.pending[seq]
 		delete(client.pending, seq)
 		client.mutex.Unlock()
 		if call != nil {
 			call.Error = err
 			call.done()
 		}
 	}
 }

 func (client *Client) input() {
 	var err error
 	var response Response
 	for err == nil {
 		response = Response{}
 		err = client.codec.ReadResponseHeader(&response)
 		if err != nil {
 			break
 		}
 		seq := response.Seq
 		client.mutex.Lock()
 		call := client.pending[seq]
 		delete(client.pending, seq)
 		client.mutex.Unlock()

 		switch {
 		case call == nil:
 			// We've got no pending call. That usually means that
 			// WriteRequest partially failed, and call was already
 			// removed; response is a server telling us about an
 			// error reading request body. We should still attempt
 			// to read error body, but there's no one to give it to.
 			err = client.codec.ReadResponseBody(nil)
 			if err != nil {
 				err = errors.New("reading error body: " + err.Error())
 			}
 		case response.Error != "":
 			// We've got an error response. Give this to the request;
 			// any subsequent requests will get the ReadResponseBody
 			// error if there is one.
 			call.Error = ServerError(response.Error)
 			err = client.codec.ReadResponseBody(nil)
 			if err != nil {
 				err = errors.New("reading error body: " + err.Error())
 			}
 			call.done()
 		default:
 			err = client.codec.ReadResponseBody(call.Reply)
 			if err != nil {
 				call.Error = errors.New("reading body " + err.Error())
 			}
 			call.done()
 		}
 	}
 	// Terminate pending calls.
 	client.reqMutex.Lock()
 	client.mutex.Lock()
 	client.shutdown = true
 	closing := client.closing
 	if err == io.EOF {
 		if closing {
 			err = ErrShutdown
 		} else {
 			err = io.ErrUnexpectedEOF
 		}
 	}
 	for _, call := range client.pending {
 		call.Error = err
 		call.done()
 	}
 	client.mutex.Unlock()
 	client.reqMutex.Unlock()
 	if debugLog && err != io.EOF && !closing {
 		log.Println("rpc: client protocol error:", err)
 	}
 }

 func (call *Call) done() {
 	select {
 	case call.Done <- call:
 		// ok
 	default:
 		// We don't want to block here. It is the caller's responsibility to make
 		// sure the channel has enough buffer space. See comment in Go().
 		if debugLog {
 			log.Println("rpc: discarding Call reply due to insufficient Done chan capacity")
 		}
 	}
 }

 // NewClient returns a new Client to handle requests to the
 // set of services at the other end of the connection.
 // It adds a buffer to the write side of the connection so
 // the header and payload are sent as a unit.
 //
 // The read and write halves of the connection are serialized independently,
 // so no interlocking is required. However each half may be accessed
 // concurrently so the implementation of conn should protect against
 // concurrent reads or concurrent writes.
 func NewClient(conn io.ReadWriteCloser) *Client {
 	encBuf := bufio.NewWriter(conn)
 	client := &gobClientCodec{conn, gob.NewDecoder(conn), gob.NewEncoder(encBuf), encBuf}
 	return NewClientWithCodec(client)
 }

 // NewClientWithCodec is like NewClient but uses the specified
 // codec to encode requests and decode responses.
 func NewClientWithCodec(codec ClientCodec) *Client {
 	client := &Client{
 		codec:   codec,
 		pending: make(map[uint64]*Call),
 	}
 	go client.input()
 	return client
 }

 type gobClientCodec struct {
 	rwc    io.ReadWriteCloser
 	dec    *gob.Decoder
 	enc    *gob.Encoder
 	encBuf *bufio.Writer
 }

 func (c *gobClientCodec) WriteRequest(r *Request, body interface{}) (err error) {
 	if err = c.enc.Encode(r); err != nil {
 		return
 	}
 	if err = c.enc.Encode(body); err != nil {
 		return
 	}
 	return c.encBuf.Flush()
 }

 func (c *gobClientCodec) ReadResponseHeader(r *Response) error {
 	return c.dec.Decode(r)
 }

 func (c *gobClientCodec) ReadResponseBody(body interface{}) error {
 	return c.dec.Decode(body)
 }

 func (c *gobClientCodec) Close() error {
 	return c.rwc.Close()
 }

 // DialHTTP connects to an HTTP RPC server at the specified network address
 // listening on the default HTTP RPC path.
 func DialHTTP(network, address string) (*Client, error) {
 	return DialHTTPPath(network, address, DefaultRPCPath)
 }

 // DialHTTPPath connects to an HTTP RPC server
 // at the specified network address and path.
 func DialHTTPPath(network, address, path string) (*Client, error) {
 	conn, err := net.Dial(network, address)
 	if err != nil {
 		return nil, err
 	}
 	io.WriteString(conn, "CONNECT "+path+" HTTP/1.0\n\n")

 	// Require successful HTTP response
 	// before switching to RPC protocol.
 	resp, err := http.ReadResponse(bufio.NewReader(conn), &http.Request{Method: "CONNECT"})
 	if err == nil && resp.Status == connected {
 		return NewClient(conn), nil
 	}
 	if err == nil {
 		err = errors.New("unexpected HTTP response: " + resp.Status)
 	}
 	conn.Close()
 	return nil, &net.OpError{
 		Op:   "dial-http",
 		Net:  network + " " + address,
 		Addr: nil,
 		Err:  err,
 	}
 }

 // Dial connects to an RPC server at the specified network address.
 func Dial(network, address string) (*Client, error) {
 	conn, err := net.Dial(network, address)
 	if err != nil {
 		return nil, err
 	}
 	return NewClient(conn), nil
 }

 // Close calls the underlying codec's Close method. If the connection is already
 // shutting down, ErrShutdown is returned.
 func (client *Client) Close() error {
 	client.mutex.Lock()
 	if client.closing {
 		client.mutex.Unlock()
 		return ErrShutdown
 	}
 	client.closing = true
 	client.mutex.Unlock()
 	return client.codec.Close()
 }

 // Go invokes the function asynchronously. It returns the Call structure representing
 // the invocation. The done channel will signal when the call is complete by returning
 // the same Call object. If done is nil, Go will allocate a new channel.
 // If non-nil, done must be buffered or Go will deliberately crash.
 func (client *Client) Go(serviceMethod string, args interface{}, reply interface{}, done chan *Call) *Call {
 	call := new(Call)
 	call.ServiceMethod = serviceMethod
 	call.Args = args
 	call.Reply = reply
 	if done == nil {
 		done = make(chan *Call, 10) // buffered.
 	} else {
 		// If caller passes done != nil, it must arrange that
 		// done has enough buffer for the number of simultaneous
 		// RPCs that will be using that channel. If the channel
 		// is totally unbuffered, it's best not to run at all.
 		if cap(done) == 0 {
 			log.Panic("rpc: done channel is unbuffered")
 		}
 	}
 	call.Done = done
 	client.send(call)
 	return call
 }

 // Call invokes the named function, waits for it to complete, and returns its error status.
 func (client *Client) Call(serviceMethod string, args interface{}, reply interface{}) error {
 	call := <-client.Go(serviceMethod, args, reply, make(chan *Call, 1)).Done
 	return call.Error
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package rpc

	import (
	"bufio"
	"encoding/gob"
	"errors"
	"io"
	"log"
	"net"
	"net/http"
	"sync"
	)

	// ServerError represents an error that has been returned from
	// the remote side of the RPC connection.
	type ServerError string

	func (e ServerError) Error() string {
	return string(e)
	}

	var ErrShutdown = errors.New("connection is shut down")

	// Call represents an active RPC.
	type Call struct {
	ServiceMethod string // The name of the service and method to call.
	Args interface{} // The argument to the function (*struct).
	Reply interface{} // The reply from the function (*struct).
	Error error // After completion, the error status.
	Done chan Call // Receives Call when Go is complete.
	}

	// Client represents an RPC Client.
	// There may be multiple outstanding Calls associated
	// with a single Client, and a Client may be used by
	// multiple goroutines simultaneously.
	type Client struct {
	codec ClientCodec

	reqMutex sync.Mutex // protects following
	request Request

	mutex sync.Mutex // protects following
	seq uint64
	pending map[uint64]*Call
	closing bool // user has called Close
	shutdown bool // server has told us to stop
	}

	// A ClientCodec implements writing of RPC requests and
	// reading of RPC responses for the client side of an RPC session.
	// The client calls WriteRequest to write a request to the connection
	// and calls ReadResponseHeader and ReadResponseBody in pairs
	// to read responses. The client calls Close when finished with the
	// connection. ReadResponseBody may be called with a nil
	// argument to force the body of the response to be read and then
	// discarded.
	// See NewClient's comment for information about concurrent access.
	type ClientCodec interface {
	WriteRequest(*Request, interface{}) error
	ReadResponseHeader(*Response) error
	ReadResponseBody(interface{}) error

	Close() error
	}

	func (client Client) send(call Call) {
	client.reqMutex.Lock()
	defer client.reqMutex.Unlock()

	// Register this call.
	client.mutex.Lock()
	if client.shutdown \|\| client.closing {
	client.mutex.Unlock()
	call.Error = ErrShutdown
	call.done()
	return
	}
	seq := client.seq
	client.seq++
	client.pending[seq] = call
	client.mutex.Unlock()

	// Encode and send the request.
	client.request.Seq = seq
	client.request.ServiceMethod = call.ServiceMethod
	err := client.codec.WriteRequest(&client.request, call.Args)
	if err != nil {
	client.mutex.Lock()
	call = client.pending[seq]
	delete(client.pending, seq)
	client.mutex.Unlock()
	if call != nil {
	call.Error = err
	call.done()
	}
	}
	}

	func (client *Client) input() {
	var err error
	var response Response
	for err == nil {
	response = Response{}
	err = client.codec.ReadResponseHeader(&response)
	if err != nil {
	break
	}
	seq := response.Seq
	client.mutex.Lock()
	call := client.pending[seq]
	delete(client.pending, seq)
	client.mutex.Unlock()

	switch {
	case call == nil:
	// We've got no pending call. That usually means that
	// WriteRequest partially failed, and call was already
	// removed; response is a server telling us about an
	// error reading request body. We should still attempt
	// to read error body, but there's no one to give it to.
	err = client.codec.ReadResponseBody(nil)
	if err != nil {
	err = errors.New("reading error body: " + err.Error())
	}
	case response.Error != "":
	// We've got an error response. Give this to the request;
	// any subsequent requests will get the ReadResponseBody
	// error if there is one.
	call.Error = ServerError(response.Error)
	err = client.codec.ReadResponseBody(nil)
	if err != nil {
	err = errors.New("reading error body: " + err.Error())
	}
	call.done()
	default:
	err = client.codec.ReadResponseBody(call.Reply)
	if err != nil {
	call.Error = errors.New("reading body " + err.Error())
	}
	call.done()
	}
	}
	// Terminate pending calls.
	client.reqMutex.Lock()
	client.mutex.Lock()
	client.shutdown = true
	closing := client.closing
	if err == io.EOF {
	if closing {
	err = ErrShutdown
	} else {
	err = io.ErrUnexpectedEOF
	}
	}
	for _, call := range client.pending {
	call.Error = err
	call.done()
	}
	client.mutex.Unlock()
	client.reqMutex.Unlock()
	if debugLog && err != io.EOF && !closing {
	log.Println("rpc: client protocol error:", err)
	}
	}

	func (call *Call) done() {
	select {
	case call.Done <- call:
	// ok
	default:
	// We don't want to block here. It is the caller's responsibility to make
	// sure the channel has enough buffer space. See comment in Go().
	if debugLog {
	log.Println("rpc: discarding Call reply due to insufficient Done chan capacity")
	}
	}
	}

	// NewClient returns a new Client to handle requests to the
	// set of services at the other end of the connection.
	// It adds a buffer to the write side of the connection so
	// the header and payload are sent as a unit.
	//
	// The read and write halves of the connection are serialized independently,
	// so no interlocking is required. However each half may be accessed
	// concurrently so the implementation of conn should protect against
	// concurrent reads or concurrent writes.
	func NewClient(conn io.ReadWriteCloser) *Client {
	encBuf := bufio.NewWriter(conn)
	client := &gobClientCodec{conn, gob.NewDecoder(conn), gob.NewEncoder(encBuf), encBuf}
	return NewClientWithCodec(client)
	}

	// NewClientWithCodec is like NewClient but uses the specified
	// codec to encode requests and decode responses.
	func NewClientWithCodec(codec ClientCodec) *Client {
	client := &Client{
	codec: codec,
	pending: make(map[uint64]*Call),
	}
	go client.input()
	return client
	}

	type gobClientCodec struct {
	rwc io.ReadWriteCloser
	dec *gob.Decoder
	enc *gob.Encoder
	encBuf *bufio.Writer
	}

	func (c gobClientCodec) WriteRequest(r Request, body interface{}) (err error) {
	if err = c.enc.Encode(r); err != nil {
	return
	}
	if err = c.enc.Encode(body); err != nil {
	return
	}
	return c.encBuf.Flush()
	}

	func (c gobClientCodec) ReadResponseHeader(r Response) error {
	return c.dec.Decode(r)
	}

	func (c *gobClientCodec) ReadResponseBody(body interface{}) error {
	return c.dec.Decode(body)
	}

	func (c *gobClientCodec) Close() error {
	return c.rwc.Close()
	}

	// DialHTTP connects to an HTTP RPC server at the specified network address
	// listening on the default HTTP RPC path.
	func DialHTTP(network, address string) (*Client, error) {
	return DialHTTPPath(network, address, DefaultRPCPath)
	}

	// DialHTTPPath connects to an HTTP RPC server
	// at the specified network address and path.
	func DialHTTPPath(network, address, path string) (*Client, error) {
	conn, err := net.Dial(network, address)
	if err != nil {
	return nil, err
	}
	io.WriteString(conn, "CONNECT "+path+" HTTP/1.0\n\n")

	// Require successful HTTP response
	// before switching to RPC protocol.
	resp, err := http.ReadResponse(bufio.NewReader(conn), &http.Request{Method: "CONNECT"})
	if err == nil && resp.Status == connected {
	return NewClient(conn), nil
	}
	if err == nil {
	err = errors.New("unexpected HTTP response: " + resp.Status)
	}
	conn.Close()
	return nil, &net.OpError{
	Op: "dial-http",
	Net: network + " " + address,
	Addr: nil,
	Err: err,
	}
	}

	// Dial connects to an RPC server at the specified network address.
	func Dial(network, address string) (*Client, error) {
	conn, err := net.Dial(network, address)
	if err != nil {
	return nil, err
	}
	return NewClient(conn), nil
	}

	// Close calls the underlying codec's Close method. If the connection is already
	// shutting down, ErrShutdown is returned.
	func (client *Client) Close() error {
	client.mutex.Lock()
	if client.closing {
	client.mutex.Unlock()
	return ErrShutdown
	}
	client.closing = true
	client.mutex.Unlock()
	return client.codec.Close()
	}

	// Go invokes the function asynchronously. It returns the Call structure representing
	// the invocation. The done channel will signal when the call is complete by returning
	// the same Call object. If done is nil, Go will allocate a new channel.
	// If non-nil, done must be buffered or Go will deliberately crash.
	func (client Client) Go(serviceMethod string, args interface{}, reply interface{}, done chan Call) *Call {
	call := new(Call)
	call.ServiceMethod = serviceMethod
	call.Args = args
	call.Reply = reply
	if done == nil {
	done = make(chan *Call, 10) // buffered.
	} else {
	// If caller passes done != nil, it must arrange that
	// done has enough buffer for the number of simultaneous
	// RPCs that will be using that channel. If the channel
	// is totally unbuffered, it's best not to run at all.
	if cap(done) == 0 {
	log.Panic("rpc: done channel is unbuffered")
	}
	}
	call.Done = done
	client.send(call)
	return call
	}

	// Call invokes the named function, waits for it to complete, and returns its error status.
	func (client *Client) Call(serviceMethod string, args interface{}, reply interface{}) error {
	call := <-client.Go(serviceMethod, args, reply, make(chan *Call, 1)).Done
	return call.Error
	}